U.S. Pat. No. 4,949,274 (Omega Engineering, Inc.), incorporated herein by reference, discloses such test meters, and in particular electronic multimeters, which measure various parameters such as electric current, voltage and resistance, via hand-held measurement probes which are brought into contact with circuits or components to be tested. The multimeters visually display the sensed signals, i.e. the measured values or test results. The multimeters disclosed in this U.S. patent also have built-in speech synthesizers enabling the meters to speak the measured values in addition to displaying them visually. The synthesizer circuitry is designed to accommodate a replaceable speech module, so that different language modules may be inserted into the meters. This allows the meter design to remain the same whilst enabling the language spoken by the meter to be changed to suit the country in which the meter is to be used.
Other forms of apparatus which incorporate speech synthesizers include vehicle navigation systems which give the driver verbal route directions, and aircraft instrument systems which give the pilot verbal warnings and instructions for corrective procedures.